The production of integrated circuits began with the creation of high-quality semiconductor wafers. During the wafer fabrication process, the wafers may undergo multiple masking, etching and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the micro-electronic structures being created on the wafer surface. As the size of the integrated circuits continues to decrease and the density of the microstructures per integrated circuit increases, the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible.
For a discussion of chemical mechanical planarization (CMP) processes and apparatus, see, for example, Arai et al., U.S. Pat. No. 4,805,348, issued February 1989; Arai et al., U.S. Pat. No. 5,099,614, issued March 1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July 1994; Karlsrud et al., U.S. Pat. No. 5,498,196 issued March 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March 1996.
Such polishing is well-known in the art and generally includes attaching one side of the wafer to a flat surface of a wafer carrier or chuck and pressing the other side of the wafer against a flat polishing surface. Polishing pads can be formed of various materials, as is known in the art, and which are available commercially. Typically, the polishing pad may be a blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Ariz. The hardness and density of the polishing pad depends on the material that is to be polished. A slurry containing a particulate abrasive such as, for example, cerium oxide, aluminum oxide, fumed/precipitated silica or other particulate abrasives may be applied to the surface of the horizontal polishing pad during polishing to enhance the polishing process.
During the polishing or planarization process, the workpiece (e.g., wafer) is typically pressed against the polishing pad surface while the pad rotates about its vertical axis. In addition, to improve the polishing effectiveness, the wafer may also be rotated about its vertical axis and oscillated back and forth over the surface of the polishing pad. It is well-known that polishing pads tend to wear unevenly during the polishing operation, causing surface irregularities to develop on the pad. To ensure consistent and accurate planarization and polishing of all workpieces, these irregularities should either be removed or accounted for.
Further, polishing pads used in CMP processes must be replaced periodically to ensure efficient polishing of workpieces (e.g., wafers). A typical CMP machine includes a polishing pad that is adhesively attached to, and covers the entire upper surface of, a heavy rotatable platen which is positioned on top of a drive assembly that is disposed within a processing chamber of the CMP machine. During the typical replacement of a polishing pad, an individual reaches into the processing chamber and grasps a portion of the polishing pad. The individual then pulls the polishing pad from the rotatable platen and discards the used polishing pad. The remaining excess adhesive which was used to affix the polishing pad to the rotatable platen must then be removed so that fresh adhesive may be applied in order to fix a new polishing pad to the rotatable platen.
In that the rotatable platen is typically two to three feet in diameter, it is difficult for an individual to perform the manipulations necessary to replace the polishing pad while the polishing pad and rotatable platen are contained within the processing chamber of the CMP machine. Accordingly, devices and apparatus for assisting in the removal and replacement of polishing pads have been conceived. For example, U.S. Pat. No. 5,551,136, issued to Bartlett, describes a tool for removing a polishing pad from a rotatable platen which includes a base, a lever member, at least one canted or angled latch pin, a chain having a plurality of links or rings, means for clamping the pad, and stop pins. Further, European Patent No. EP 0 850 726 A1, published Jul. 1, 1998 and assigned to Applied Materials, Inc., discloses a method and apparatus for automatically changing a polishing pad and a chemical mechanical polishing system. In brief, a mechanical device is placed against a used polishing pad on a platen in a CMP system and a lifting mechanism, such as a pneumatic actuator, may be used to lift the used polishing pad from the platen. The mechanical device and used polishing pad move to a used pad receptacle and the pad is released from the chemical device and deposited into the receptacle. The mechanical device is then placed against a new polishing pad in a pad dispenser and the pad is chucked to the mechanical device by a vacuum pump. The mechanical device and pad are then moved toward the polishing platen and the pad is released from the mechanical device onto the platen.
Although the previously described methods and apparatus for replacing a polishing pad are designed to facilitate the process of replacing a polishing pad in CMP processing and increase the efficiency in replacing a polishing pad, they each require the introduction of a second device or apparatus which includes multiple moving parts thereby introducing additional elements and features which may become worn and/or require maintenance. The introduction of such a second apparatus or device in facilitating the replacement of a polishing pad also significantly increases the cost of the CMP process as well as the downtime for the CMP equipment.
Accordingly, there is a need for a simple method and apparatus which facilities the removal and replacement of a polishing pad during CMP processing that decreases down time and increases throughput without significantly increasing the cost, wear and maintenance of components used in the removal and replacement of polishing pads.